This invention relates to a new cutting oil useful for the working of nonferrous metals by cutting. In particular, it relates to a cutting oil for milling and/or engraving copper cylinders employed in gravure printing.
There is a great demand for efficient cutting oils for the working of metals, in particular nonferrous metals, by cutting, such as lathing, milling, boring, sawing, cutting and grinding. These oils serve as coolants and lubricants and have the purpose of ensuring problem-free working of the workpiece. In particular, they should enable the cutting tool to slip easily over the workpiece and the heat generated locally during the cutting to be removed. They also should prevent corrosion of the worked surface of the metal and wearing of the tool. (See, e.g., Ullmann's Enzyklopaedie der technischen Chemie (Ullmann's Encyclopedia of Industrial Chemistry), 4th edition, volume 20, pages 617-622, 1981).
In gravure printing, the print image is engraved on the outer surface of the copper impression cylinder in the form of corresponding depressions. These depressions take up the printing ink during the printing operation, and the ink is then transferred from the rotating cylinder onto the material to be printed. When printing has ended, this outer engraved layer of copper is removed from the used cylinder by a milling operation. A new print image is then engraved in the fresh surface and this is coppered or chromed in order to achieve a higher mechanical strength (necessary in the case of high print runs).
The mentioned milling operation predominantly uses a special apparatus which mills the outer layer of metal, which is no longer required, from the rotating copper cylinder with high precision by means of a high-speed milling disk fitted with cutting diamonds.
This process requires a cutting oil which should fulfill the following requirements:
1. It should enable problem-free working of the impression cylinder, i.e.,
(a) formation of an oil film which adheres well and does not break even during the milling operation and the relatively high temperatures thereby produced, PA1 (b) production of an absolutely smooth, new surface by correspondingly good lubrication of the cutting tool, PA1 (c) good removal of heat from the worked metal surface and the cutting tool, PA1 (d) prevention of agglomeration of the milled metal particles, especially on the cutting tool, and PA1 (e) prevention of corrosion of the fresh metal surface and of rapid wear of the cutting tool.
2. During subsequent engraving of the copper cylinder, the gliding foot of the engraving unit must slide perfectly over the cutting oil film.
3. After the engraving, it must be possible to remove the cutting oil film completely in an alkaline degreasing bath. Only then is there ensured a sufficient adhesion of the layer of metal applied during subsequent coppering or chroming of the engraved surface of the impression cylinder and hence a high print run of constant print quality.
The cutting oils hitherto used according to the prior art usually consist of a natural fat, i.e., a glycerol ester of natural, partially unsaturated fatty acids (content in the cutting oil: about 50% by weight), dissolved in chlorinated hydrocarbons (usually a mixture of methylene chloride and trichloroethane).
The disadvantages of this oil are many. For example:
A. An impression cylinder treated with this product can be degreased completely only with great difficulty. Especially at the edges of the cylinder, removal of the oil by the degreasing bath is only incomplete. This leads to poor adhesion of the freshly deposited copper or chromium layers. Cylinder and machine damage and thus, finally, lower print runs and poorer print quality result.
B. Because of the content of chlorinated hydrocarbons of high vapor pressure, the cutting oil according to the prior art is a health hazard. Application of the cutting oil as a thin film to the cylinder also promotes evaporation. Thus, the personnel employed in this operation are exposed to a high level of chlorinated hydrocarbons in the air which they breath. Frequently, the level reaches a point where it is no longer tolerable.
C. The high-speed milling disk (up to about 10,000 revolutions per minute) causes misting of the cutting oil. This leads to undesirable pollution of the work station and an odor nuisance to the personnel employed there. There also results further deterioration and danger from the spray mist and the oil precipitated.